FIELD OF THE INVENTION
The invention relates to a semiconductor laser device having a multiplicity of individual lasers disposed in a laser-active region within outer boundary surfaces, including front and rear boundary surfaces extending crosswise to an exit direction of the laser light, and lateral, bottom and top boundary surfaces extending parallel to the exit direction of the laser light.
In laser diodes, and particularly in high-power laser diodes, the appearance of low-loss internal ring modes, or other concurrence modes, which sometimes interfere considerably with the desired laser operation and which as a rule are induced by spontaneously emitted photons, superluminescence or scattered laser radiation, leads to an impairment in overall efficiency of the laser diodes. The influence of such problems occurs particularly for short resonator lengths (such as less than about 300 .mu.m and/or at a provided front-sided dereflection layer, particularly in products wherein the mirror reflections R.sub.front .multidot.R.sub.back are less than approximately 0.30). This problem has been made even worse with the increasing improvement in the epitaxial layers used in semiconductor laser devices to form the laser-active regions, because the internal absorption and scattering losses of the boundary layers are even lower. In this respect, it has become known heretofore from the literature in Appl. Phys. Lett. 52 (16) pp. 1320 ff., 1988, that quite a considerable proportion of the degradation mechanisms is photon-induced, especially in GaAs/AlGaAs semiconductor laser diodes. For this reason, the interfering photons mentioned are also definitively involved in the aging of the laser diode.
In laser diodes with wide active regions and therefore a great tendency to the aforementioned vulnerability to interference or malfunction, the active region is split by dividing trenches into a multiplicity of narrower active regions. In laser diodes with relatively wide individual regions (for example, 40 laser strips with a total width of 400 .mu.m) or short resonator lengths and/or mirror reflections with R.sub.front .multidot.R.sub.back .ltoreq.0.30, this provision is generally no longer adequate. In multilaser arrays, the problem has therefore been countered in the past in such a way that the lateral boundaries of the laser-active region, embodied as V-shaped trenches, were provided with a material which absorbs or decouples the undesired transverse or ring modes of the laser radiation (note the published European Patent Document EP-A 221 285 B1). If the laser mirror coating were selected so that R.sub.front .multidot.R.sub.back .gtoreq.0.3, then the absorptive property of, for example, a titanium coating or also a chromium coating in the etched lateral dividing trenches sufficed to suppress the competing modes.
Other multilayer arrays have been disclosed, for example, in U.S. Pat. No. 4,792,200 or U.S. Pat. No. 5,063,570.
With the invention, all the photons which in any way interfere with the desired laser operation are eliminated entirely or at least in part, with the goal of improving all the essential characteristic laser properties, such as threshold current, differential steepness or gradient, mirror destruction or disruption limit, spectral mode behavior, and aging.